Field of the Invention
The present invention relates to the microbiological industry, and specifically to a method for producing L-amino acids by fermentation of a bacterium of the family Enterobacteriaceae which has been modified to overexpress the yajL gene.
Brief Description of the Related Art
Conventionally, L-amino acids are industrially produced by fermentation methods utilizing strains of microorganisms obtained from natural sources, or mutants thereof. Typically, the microorganisms are modified to enhance production yields of L-amino acids.
Many techniques to enhance L-amino acids production yields have been reported, including transformation of microorganisms with recombinant DNA (see, for example, U.S. Pat. No. 4,278,765 A) and alteration of regulatory regions such as a promoter, leader sequence, and/or attenuator, or others known to the person skilled in the art (see, for example, US20060216796 A1 and WO9615246 A1). Other techniques for enhancing production yields include increasing the activities of enzymes involved in amino acid biosynthesis and/or desensitizing the target enzymes to the feedback inhibition by the resulting L-amino acid (see, for example, WO9516042 A1, EP0685555 A1 or U.S. Pat. Nos. 4,346,170 A, 5,661,012 A, and 6,040,160 A).
Another method for enhancing L-amino acid production yields is to attenuate expression of a gene or several genes which are involved in degradation of the target L-amino acid, genes which divert the precursors of the target L-amino acid from the L-amino acid biosynthetic pathway, genes involved in the redistribution of the carbon, nitrogen, and phosphate fluxes, and genes encoding toxins, etc.
The yajL gene encodes the YajL protein which belongs to the PfpI/Hsp31/DJ-1 superfamily that includes chaperones, peptidases, and the protein DJ-1 (Messaoudi N. et al., Global stress response in a prokaryotic model of DJ-1-associated Parkinsonism, J. Bacteriol., 2013, 195(6):1167-1178). The YajL is the closest prokaryotic homolog of DJ-1. For example, the Escherichia coli (E. coli) YajL protein has 40% sequence identity and a similar three-dimensional structure with human DJ-1, an oncogene and neuroprotective protein whose loss-of-function mutants are associated with certain types of familial, autosomal recessive Parkinsonism (Wilson M. A. et al., The atomic resolution crystal structure of the YajL (ThiJ) protein from Escherichia coli: a close prokaryotic homologue of the Parkinsonism-associated protein DJ-1, J. Mol. Biol., 2005, 353(3):678-691). The high homology and similarity of crystal structures of YajL and DJ-1 suggest that the proteins have similar function. It was found recently that YajL protects bacteria against oxidative stress and oxidative-stress-induced protein aggregation possibly through its chaperone function and control of gene expression (Kthiri F. et al., Protein aggregation in a mutant deficient in YajL, the bacterial homolog of the Parkinsonism-associated protein DJ-1, J. Biol. Chem., 2010, 285:10328-10336). In E. coli, YajL functions as a covalent chaperone that, upon oxidative stress, forms mixed disulfides with chaperones, proteases, ribosomal proteins, catalases, peroxidases, and FeS proteins (Messaoudi N. et al., J. Bacteriol., 2013, 195(6):1167-1178).
Until now, no data has been reported demonstrating the effect from overexpression of the yajL gene on L-amino acid production by the modified bacterial strains of the family Enterobacteriaceae.